Ask them for specifics as to why they think you need this centering. What is the load capacity at 16 inch, then what is the load capacity at 12 inch. Do you need this added capacity. Selling someone an open trailer that they are going to stuff can mean they want to be on the safe side, as they’re not sure what your going to do. By using the load capacities you are working from known numbers, not statements like a brick ***house. The only other advantage to smaller centers, especially if you are cutting openings yourself, is it gives you more flexibility as to their size if you cut openings within the open areas of the supports.